Not a fan of 2400 myself; I've never found an application for it that another powder couldn't do better. As a replacement for Unique, you can expect more flash, blast, and recoil to generate the same velocity.
WSF is my favorite Unique substitute. It burns relatively clean, and meters nicely, being a ball powder. In all the loads I've tried, the velocity numbers match Unique grain for grain.
Universal Clays is a close second favorite, and gives me a little better accuracy in 45 Auto loads than the equivalent load of Unique. Charge weights are pretty similar as well.
